code: def test_assign_with_empty_priors(self):
      assigner = GridAssigner(pos_iou_thr=0.5, neg_iou_thr=0.3)
      pred_instances = InstanceData(
          priors=torch.Tensor(torch.empty(0, 4)),
          responsible_flags=torch.empty(0),
      )
      gt_instances = InstanceData(
          bboxes=torch.Tensor([[23, 23, 43, 43]]),
          labels=torch.LongTensor([0]),
      )
  
      assign_result = assigner.assign(
          pred_instances=pred_instances, gt_instances=gt_instances
      )
      expected_gt_inds = torch.LongTensor([])
      assert_allclose(assign_result.gt_inds, expected_gt_inds)
  
file_path: mmdetection/tests/test_models/test_task_modules/test_assigners/test_grid_assigner.py
imports: from unittest import TestCase
  import torch
  from mmengine.structures import InstanceData
  from mmengine.testing import assert_allclose
  from mmdet.models.task_modules.assigners import GridAssigner
label_desc: Use image node_id 3 for calling the TestGridAssigner obj's underlying member method code with example usage: obj.test_assign_with_empty_priors() without return types